This P30 application seeks the competitive renewal of the Center for AIDS Intervention Research (CAIR) at the Medical College of Wisconsin as an HIV behavioral research center. Through its history, CAIR's thematic mission has been the conceptualization, conduct, and rigorous evaluation of HIV primary and secondary prevention interventions, and the dissemination of research findings to both the scientific community and service providers. The P30 Center structure has brought together and supports the efforts of a multidisciplinary team of HIV prevention investigators, and CAIR has functioned as a highly-productive and strong regional, national, and international resource in the areas of research, training, and service to public health providers. Center investigators have made substantial contributions in the conduct of HIV primary and secondary prevention interventions with vulnerable populations in the United States, have initiated important new international initiatives in Eastern Europe and other regions, have advanced our scientific knowledge of how to transfer research-based prevention models to service providers nationally and internationally, and have undertaken vigorous research lines of basic behavioral and social science, methodological, and cost-effectiveness research applied to HIV prevention. To support continued excellence in these and other emerging new areas that we will pursue in the years ahead, we propose a structure that continues to bring together teams of interdisciplinary scientists and provides resources in the following Core areas: the Administration Core, responsible for scientific and administrative leadership of the Center; the Developmental Core, which supports preliminary studies, internal peer review, and Center seminars and conferences; the Qualitative Methods Core, which provides qualitative and social science supports to CAIR investigations; the Intervention Research Support and Dissemination Core, with functions that meet support needs of intervention studies and transfers research advances to service providers and others outside CAIR; the International Research Support Core, which facilitates Center international initiatives; the Quantitative Core, with resources that support centralized data management, analysis, and biostatistical consultation; and the Cost-Effectiveness Studies Core, which supports the conduct of HIV prevention cost-effectiveness and economic evaluation research. This Core structure, which grows out of our experience as a P30, is proposed because it meets the needs of current studies of CAIR investigators and studies in areas that we foresee as important in the field over the next five years.